Muhammad Ali and other celebrities took to Twitter before Saturday's Floyd Mayweather vs. Manny Pacquiao fight in Las Vegas.

The bout, one of the most heavily anticipated in boxing history, will take place at the MGM Grand Garden Arena in Las Vegas. Start time is expected about 11:30 p.m. ET, after the main pay-per-view undercard begins at 9 p.m.

Mayweather (47–0, 26 KOs) has his WBC and WBA titles on the line. The 38-year-old fighter last took the ring in September, landing a unanimous decision in his rematch with Marcos Maidana.

Pacquiao (57–5–2), meanwhile, will defend his WBO title. The 36-year-old last defeated Chris Algieri in December, also in a unanimous decision.